Lab / experiment Grade 8 Science
Rookery Field Soil Infiltration: Sand, Loam, and Clay Rates
A grade 8 science lab where students time how fast water passes through sand, loam, and clay, calculate infiltration rates, and connect them to recharge and runoff.
Objectives
- Students will measure how long water takes to pass through three soil types and calculate an infiltration rate for each.
- Students will use their rates to explain which ground cover produces more runoff and which recharges groundwater.
Vocabulary
- Infiltration
- Infiltration is when rain or melted snow soaks down into the soil instead of flowing away across the top of it. Water that infiltrates can feed plant roots or keep sinking to become groundwater.
- Recharge
- Recharge is water soaking down through the ground to refill an aquifer, the way rain refills an underground sponge. Aquifers stay healthy only if recharge keeps up with pumping.
- Permeability
- Permeability describes how easily water can move through a material. Water flows quickly through gravel but very slowly through clay, even though both can hold water.
Also: runoff
Teacher overview
When rain falls on the fictional Rookery Field, some of it soaks into the ground and refills the aquifer while the rest runs off the surface. How much goes each way depends on what the ground is made of. This lab has students pour equal amounts of water through columns of sand, loam, and clay, time how long the water takes to pass through, and turn those times into infiltration rates they can compare. The results connect a simple measurement to two big ideas: groundwater recharge and stormwater runoff.
Procedure
Build three test columns. An adult cuts the bottom off three identical clear bottles. Turn each bottle upside down to use as a funnel, set a coffee filter in the neck, and stand each funnel in a collecting cup on the tray.
Add equal soil samples. Fill each funnel with the same packed depth of one material: sand in the first, loam in the second, and clay-rich soil in the third. Press each sample down the same amount so the only difference is the type of soil.
Pour and time the first trial. Pour 200 mL of water into the sand column and start the stopwatch the moment the water hits the soil. Stop timing when the water has finished draining into the cup, and record the time in seconds. Repeat for the loam and clay columns.
Run a second trial. Empty the collecting cups and pour a fresh 200 mL through each column again, recording a second time for each material to check whether the results are consistent.
Safety note. Do not drink or taste any of the water or soil, wipe up spills right away so no one slips, and let the adult handle the bottle cutting.
Data & Analysis
| Material | Trial 1 time (s) | Trial 2 time (s) | Average time (s) |
|---|---|---|---|
| Sand | |||
| Loam | |||
| Clay |
- Which material let the 200 mL of water pass through fastest, based on your average times?
- For each material, calculate an infiltration rate using rate = volume poured ÷ average time. Show the setup for at least one material.
- A group poured 200 mL onto their sand column and it drained through in 25 seconds. What was the infiltration rate in mL per second?
- The same group's clay column took 200 seconds for the same 200 mL. What was its infiltration rate in mL per second?
- Using your answers to questions 3 and 4, how many times faster did the sand infiltrate than the clay?
- During a heavy storm, which material would produce the most runoff, and which would let the most water recharge the groundwater? Use your rates to explain.
- A parking lot is paved over sandy ground at Rookery Field. Predict how that paving changes infiltration and runoff, and suggest one way to reduce the extra runoff.
- Explain how infiltration connects to the part of the water cycle that refills aquifers.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
- Answer: Sand. In almost every class set, sand has the shortest average time, meaning water passes through it fastest; accept the material with the lowest average from the student's own data.
- Answer: Rate = 200 mL ÷ average time for each material, giving a value in mL per second. Accept any rates that match the student's recorded average times, with faster materials showing larger rates.
- Answer: 8 mL per second. 200 mL ÷ 25 seconds = 8 mL/s.
- Answer: 1 mL per second. 200 mL ÷ 200 seconds = 1 mL/s.
- Answer: 8 times. 8 mL/s ÷ 1 mL/s = 8, so the sand infiltrated eight times as fast as the clay.
- Answer: Clay produces the most runoff because water passes through it slowly, so most stays on the surface; sand recharges the most groundwater because water moves through it quickly. Accept answers that correctly use the student's own rate comparison.
- Answer: Paving seals the surface, so infiltration drops to nearly zero and almost all the rain becomes runoff. Accept reduction ideas such as adding a rain garden, permeable pavement, or a swale that lets water soak in.
- Answer: Infiltration is the step where water soaks down through soil and rock into the aquifer, so it is the recharge pathway of the water cycle that refills the groundwater people pump for wells.
Differentiation
Support
Pre-build the three columns before class so students focus on pouring and timing, and give a data table with the infiltration-rate formula already written at the bottom. Run one material together as a class first.
Extension
Have students test a fourth column that mixes two materials, predict where its rate will fall relative to the pure samples, and then check the prediction against their measured average time.
ELL supports
Label each material and each step with a small picture, and provide the sentence frame "Water moved through ___ fastest because ___" for the analysis questions. Allow students to report rates as numbers with a labeled arrow rather than full sentences.